Journal of Geosciences, 65 (2020), 153–172

DOI: 10.3190/jgeosci.307

Original paper

Beryllium minerals as monitors of geochemical evolution frommagmatic to hydrothermal stage; examples from NYF pegmatitesof the Třebíč Pluton, Czech Republic
Adam ZACHAŘ*, Milan NOVÁK, Radek ŠKODA
Department of Geological Sciences, Faculty of Sciences, Masaryk University, Kotlářská 2, Brno 611 37, Czech Republic;
adamzachar@seznam.cz*
Corresponding author
Mineral assemblages of primary and secondary Be-minerals were examined in intraplutonic euxenite-type NYF pegmatites of the Třebíč Pluton, Moldanubian Zone occurring between Třebíč and Vladislav south of the Třebíč fault.
Primary magmatic Be-minerals crystallized mainly in massive pegmatite (paragenetic type I) including common beryl I,
helvite-danalite I, and a rare phenakite I. Rare primary hydrothermal beryl II and phenakite II occur in miarolitic pockets(paragenetic type II). Secondary hydrothermal Be-minerals replaced primary precursors or filled fractures and secondary
cavities, or they are associated with ,,adularia” and quartz (paragenetic type III). They include minerals of bohseite-bavenite series, less abundant beryl III, bazzite III, helvite-danalite III, milarite-agakhanovite-(Y) III, phenakite III, anddatolite-hingganite-(Y) III. Chemical composition of the individual minerals is characterized by elevated contents of
Na, Cs, Mg, Fe, Sc in beryl I and II; Na, Ca, Mg, Fe, Al in bazzite III; REE in milarite-agakhanovite-(Y) III; variations
in Fe/Mn in helvite-danalite and high variation of Al in bohseite-bavenite series. Replacement reactions of primary Be-minerals are commonly complex and the sequence of crystallization of secondary Be-minerals is not defined; minerals
of bohseite-bavenite series are mostly the latest. Beryl usually occurs in pegmatites with rare tourmaline, whereas helvite-danalite bearing pegmatites are tourmaline-rich. Abundant tourmaline in pegmatites with helvite-danalite and its scarcity
in beryl-bearing pegmatites indicate that early tourmaline crystallization affected activity of Al in the parental medium
and thus may have controlled formation of primary Be-minerals (beryl – higher Al, helvite-danalite – lower Al) which
crystallized later. Secondary Be-minerals with dominant minerals of bohseite-bavenite series and milarite suggest highactivity of Ca in fluids. Variations in chemical composition (Al contents) of bohseite-bavenite series were controlled by
the chemical composition of the precursor. High variability of primary magmatic Be-minerals within a single pegmatite
district is exceptional and it is constrained by variable activities of Si and mainly Al, divalent cations – Ca, Mn, Fe, Zn
and Mg, trivalent cations – REEs, Sc, and B, S, and fO2 in the individual pegmatites.
Keywords: beryl, phenakite, helvite-danalite, milarite- and gadolinite-group minerals, bohseite-bavenite, NYF pegmatites, Třebíč Pluton
Received: 15 April 2020; accepted: 21 July 2020; handling editor: J. Sejkora
The online version of this article (doi: 10.3190/jgeosci.307) contains supplementary electronic material.

1. Introduction
Beryllium minerals are typical accessory phases in granitic pegmatites of almost all classes/types defined by Černý
and Ercit (2005) with beryl as by far the most abundantprimary Be-mineral (e.g., Černý 2002; London 2008).
Minor to very rare primary Be-minerals that comprisephenakite, chrysoberyl, gadolinite-, helvite- and rhodizite-group minerals, beryllonite, hurlbutite, hambergite(Černý 2002 and references therein), and primary milarite(Novák et al. 2017) also occur in granitic pegmatites
commonly associated with beryl. Primary Be-minerals
used to be very often altered to numerous secondary Beminerals as, e.g., bertrandite, bavenite, phenakite, bityite,and milarite (Černý 2002).
High incompatibility of Be in major and most minor
and accessory minerals from granitic rocks, caused by thesmall ionic size and low charge of Be2+, facilitated existence of a broad suite of Be minerals; about 115 minerals
with a substantial content of Be, have been described(e.g., Hawthorne and Huminicki 2002; Grew and Hazen
2014). Because of externally imposed chemical potentials
that govern the stability of Be-minerals (Barton 1986),
the individual Be-minerals may thus serve as sensible
geochemical mineral indicators. They can be utilizedon this purpose from primary magmatic to secondaryhydrothermal stages of granitic pegmatites (e.g., Burt
1978; Markl and Schumacher 1997; Černý 2002; Barton
and Young 2002; Franz and Morteani 2002).
Granitic pegmatites of the Třebíč Pluton are a specific type of NYF-affiliated, and they are mostly F-poor
pegmatites, which have been derived from ultrapotassic
I-type orogenic pluton (Martin and de Vito 2005; Novák
et al. 2012; Čopjaková et al. 2013). Beryllium minerwww.jgeosci.org

Adam Zachař, Milan Novák, Radek Škoda

2. Geological setting

15°50’

BOHEMIANMAS
PRAGUE

BRNO

49°25’VELKÉ MEZIŘÍČÍ

49°10’

2.1. Třebíč Pluton
The parental granite (melagranite to melasyenite–durbachite) of the examined pegmatites is one of durbachitevaugnerite bodies typical for the European Variscan
orogeny (e.g., von Raumer et al. 2014). It forms a large
flat body located in the eastern part of the MoldanubianZone (Fig. 1a; Leichmann et al. 2017). The rock is dominantly coarse-grained, porphyritic, and foliated to various
degrees near its contacts with host metamorphic rocks. It
is built up of large phenocrysts of orthoclase. Additional
minerals comprise (Fe, Ti)-rich phlogopite, oscillatoryzoned plagioclase (An8–40), amphibole (actinolite torare magnesiohornblende), and quartz, forming mostly
a medium-grained matrix. Typical accessory minerals
include fluorapatite, zircon, allanite-(Ce), titanite, andsulfide minerals.
The bulk composition of durbachite is characterized
by the metaluminous signature (ASI = 0.85–0.93), highconcentrations of K2O (5.2–6.5 wt. %), MgO (3.3–10.4
wt. %), P2O5 (0.47–0.98 wt. %), Rb (330–410 ppm), Ba(1100–2470 ppm), U (6.7–26.2 ppm), Th (28.2–47.7ppm), Cr (270–650 ppm), Cs (20–40 ppm), a highK/Rb (133–171), but low CaO (2.3–4.8 wt. %) and Srcontents, and a high Rb/Sr (0.8–1.3). The concentrations of Be (6–9 ppm) and B (9–20 ppm) are similar
to ordinary granites (e.g., London and Evensen 2002).
Both geochemical signature, as well as the isotopic Sr(87Sr/86Sr337 = 0.709–0.7125) and Nd (337Nd = –6.3) datasuggest mixing of a durbachitic magma with (leuco)granitic melt derived from crustal rocks undergoing anatexis
during rapid decompression (for details, see, e.g., Holub
1997; Janoušek et al. 2003; Breiter 2008; Janoušek et al.
2019). Radiometric dating of the durbachite (U/Pb zir154

FSI

als, including primary magmatic, primary hydrothermaland secondary hydrothermal beryl, bazzite, phenakite,helvite-danalite, milarite-group minerals, gadolinitegroup mineral, and bohseite-bavenite series occur insome intragranitic euxenite-type pegmatites (Staněk
1973; Škoda et al. 2006; Novák and Filip 2010). Mixed
NYF–LCT Li-bearing pegmatite of Kracovice contains
primary hambergite and secondary beryl, bavenite, andbertrandite (Němec 1990; Novák et al. 1998). We examined mineral assemblages, textural relations and chemicalcomposition of Be-minerals from euxenite pegmatites toreveal conditions of their origin, including activities ofvarious elements from primary magmatic to the secondary hydrothermal stage. Also, mineral assemblages ofprimary Be-minerals from various granitic pegmatites
were discussed.

durbachite
pegmatite-rich areas
KRA Be-rich pegmatites

N
Drosendorf unit
Gföhl unit
low-grade schists
5 km
faultsFig. 1 Simplified geological map of Třebíč Pluton with marked positionof studied pegmatites: TER – Terůvky; KOZ – Kožichovice I,II; POZ– Pozďátky; KLU – Klučov III; OKR – Okrašovice; CIM – Číměř I,II;KRA – Kracovice.

con) yielded ages of 342–335 Ma (Janoušek et al. 2020
and references therein).

2.2. Granitic pegmatites
Pegmatites of the Třebíč Pluton have been divided basedon their mineral assemblages, degree of geochemical
fractionation and internal structure into several groups:(i) geochemically primitive allanite-type pegmatites, and(ii) more evolved euxenite-type pegmatites (Novák et al.
1999, 2012; Škoda et al. 2006; Škoda and Novák 2007;
Zachař and Novák 2013). (iii) The highly evolved, Li,
REE-bearing pegmatite from Kracovice, the only known
extragranitic pegmatite, which cuts gneisses ~0.5 km
to the W of the Třebíč Pluton (Němec 1990; Novák etal. 1999, 2012) has not been examined. The first two
pegmatite types relate to the REL-REE subclass, a rareelements class of the NYF family (Černý and Ercit 2005).
Nevertheless, they are F-poor and do not entirely fit thedefinition of NYF family (Simmons et al. 2012), whereas
the (iii) Kracovice represents mixed NYF-LCT pegmatite

Beryllium minerals from NYF pegmatites of the Třebíč Pluton(Novák et al. 1999; Černý and Ercit 2005; Novák et al.
2012; Čopjaková et al. 2015). Martin and De Vito (2005)
considered pegmatites of Třebíč Pluton to be NYFrelated, and to a specific type of pegmatite derived fromultrapotassic orogenic pluton belonging to a shoshonitic
association (see Žák et al. 2005).
The euxenite-type pegmatites form subverticallyzoned dikes, ~0.2–1 m thick, and typically show a transitional contact with the host durbachite. Their internal
structure comprises (from the contact inward): a border/
wall zone of medium- to coarse-grained granitic unit
(Kfs+Qz+Plg+Phl±Amp±Tur), a graphic unit (Kfs+Qz> Ab+Qz), a blocky K-feldspar unit (locally pale green
amazonite) and a quartz core (Fig. 2). A medium- tocoarse-grained albite unit is locally found in nests, up to
10 cm in diameter, typically developed between blocky
K-feldspar and quartz core. Rare small pockets withcrystals of quartz, K-feldspar, and albite were found insome dikes. Along with the aforementioned phlogopite,
most pegmatites contain minor to rare accessory black
tourmaline (Ca, Ti-rich, Al-poor schorl-dravite; Novák
et al. 2011) and common to rare accessory minerals.
These include titanite, allanite-(Ce), pyrite, ilmenite, pseudorutile, niobian rutile, zircon, REE, Nb, Ta,
Ti-oxide minerals, and beryl (Novák and Čech 1996;Škoda et al. 2006; Škoda and Novák 2007; Novák andFilip 2010). The euxenite-type pegmatites with Beminerals are located exclusively south of the Třebíč
fault in the W–E trending belt from Třebíč to Vladislav(Fig. 1b). Unfortunately, a flat landscape in the area of
the Třebíč Pluton provided only several well-exposed
outcrops, and some Be-minerals are known only in rockfragments from agricultural fields. Chemical compositionof the individual units of the euxenite-type is characterized by high Si (75.74–76.51 wt. % SiO2), moderate Al(13.04–13.08 wt. % Al2O3), ASI (1.02–1.09), dominanceof K2O over Na2O (5.58–7.46 wt. %, 2.55–3.25 wt. %,respectively), low CaO (0.11–0.78 wt. %) and very low
P2O5 (0.02 wt. %). Trace elements gave Ba (197–947ppm), Rb (222–297 ppm), U (3.5–28.6 ppm) and Th(15.4–31.6 ppm), Be (11–42 ppm), B (24–68 ppm) andF (90–110 ppm) (Čopjaková et al. 2013).

3. Samples and methods
The samples studied in detail come from the field research of the authors starting in early 2000ies, including
very recently (2016–2019) discovered localities (Číměř I,Číměř II, Okrašovice, and Klučov III). Only a smallpart of the samples was taken from the collection of theMoravian Museum, Brno, collected in the 1950ies to
1980ies. They represent unique mineral assemblages of
Be-minerals; however, some are known only from frag-

100 cmQ
hostdurbachite
granitic unit
aplitic unit
graphic unit
blocky K-feldspar
Qquartz coretransitional contact with host rockFig. 2 Simplified cross-section of euxenite pegmatite from Třebíč Pluton. Slightly modified from Škoda et al. (2006).

ments and geology, and mineral assemblages of theirparental pegmatite bodies are poorly known.
Used terms: for examined and associating minerals intext and figures following abbreviations have been used.
Boh = bohseite, Bvn = bavenite, Bz = bazzite, Hlv =helvite (-danalite), Mil = milarite, Ph = phenakite. Other
abbreviations are after Whitney and Evans (2010).

3.1. Electron-probe microanalysis (EPMA)
Chemical compositions of studied minerals were determined by means of the Cameca SX100 electron
microprobe at the Laboratory of Electron Microscopy
and Microanalysis, Department of Geological Sciences,
Masaryk University, Brno in wavelength dispersive modeand the accelerating voltage 15 kV, beam current 10 nA
and a spot size ~5 μm. The following standards and X-ray
Kα lines were used: sanidine (Si, Al, K), albite (Na), olivine (Mg), wollastonite (Ca), almandine (Fe), spessartine(Mn), fluorapatite (P), titanite (Ti), chromite (Cr), topaz(F), gahnite (Zn), SrSO4 (S). The peak counting timewas 10 seconds for major elements and 20–40 seconds
for minor to trace elements. The background counting
time was 1/2 of the peak counting time on the high- andlow-energy background-position. Raw intensities werecorrected for matrix effects using the X-PHI algorithm(Merlet 1994). The theoretical amount of unanalyzed
155

Adam Zachař, Milan Novák, Radek Škoda

light elements (H, Be, B) was included in the matrix
correction procedure. For analysis of REE-bearing minerals, the conditions described in Novák et al. (2017), andŠkoda et al. (2018) were used.
Results obtained from EPMA were calculated as following: T = 6 atoms (beryl group); Si = 3 apfu (helvite
group); Si = 2 apfu, B = Ca, Be = 2–B (gadolinite group);
Si = 12 apfu (milarite group); Si = 9 apfu (bohseitebavenite series).

3.2. Rare Earth Elements terminology
According to the International Union for Pure and Applied Chemistry, the term rare-earth elements (REEs)
includes lanthanoids (Ln), yttrium (Y), and scandium(Sc). Due to the substantially smaller ionic radius of Sc
concerning the rest of the group, it frequently enters different crystal-structural sites via different substitutions.
Therefore, Sc is commonly not included in the REEs ingeological sciences, and neither in this paper. Due to thelanthanide contraction phenomenon, the REEs are further

divided into larger LREE (light Ln, La–Gd) and smaller
HREE (heavy Ln, Tb–Lu, and Y).

4. Results

4.1. Mineral assemblages of the examinedpegmatites
The internal structure, as well as the shape and size ofthe examined euxenite pegmatite dikes with Be-minerals(Tab. 1), are similar to the pegmatites described in thesubchapter 2.2. (see also Škoda et al. 2006; Novák andFilip 2010; Novák et al. 2011; Čopjaková et al. 2013).
Accessory minerals, including primary Be-minerals fromthe examined localities, are given in Tab. 1. Tourmaline is
the most abundant minor to accessory mineral along withmajor constituents – feldspars and quartz (Tab. 1). It isvery rare or even absent in beryl-bearing pegmatites, and,on the other hand, abundant in helvite-danalite bearing
pegmatites. The following textural-paragenetic types ofTab. 1 Primary minor and accessory minerals from the examined pegmatites
FamilyPegmatite
type

Mineralassemblage

allaniteBP
assemblage

NYF
euxenite

HDP
assemblage

NYF+LCT

Locality(abbreviation)

Field setting

Primary
Be-minerals

Tourmaline

Micas

many

outcorps/blocks

absentabsent to +++Bt

Vladislav

outcropabsent+Bt

Okrašovice (Okr)large blocks

beryl I++

Bt

Kožichovice I(KozI)

outcropberyl I+

Bt

Kožichovice II(KozII)

outcropPozďátkyTerůvky (Ter)fragment
fragment

Klučov III (KluIII)

outcropČíměř II (CimII)

outcropČíměř I (CimI)

outcrop

helvite I>
phenakite I>> beryl I+++

Kracovice (Krc)outcrophambergite+++

beryl I>>
phenakite I
beryl II
phenakite II
helvite I>
phenakite I
helvite I

AccessorymineralsAln, Ttn,
Zrn, Ilm
EGM, Aln,Mnz, Ilm,
Zrn
EGM, Aln,
Ilm, Zrn
Ilm

+

Bt

+
?

?
?

AGM,
Nb-rutile,
CGM, Py,
Aln, Ttn,
Ilm, Zrn
Ilm
?

+++

Bt

AGM, Cst+++

Bt

References
1, 2, 3, 4
1, 2
4
this study

3, 5

this study
6
this studyAlnthis study
AGM, Cst,
CGM, Apy,
Bt
this study
Po, PGM,
Zrn
FGM, SGM,
Aln, Sps,
Lpd,
Tpz, Mnz, 7, 8, 9, 10, 11
Ms, BtXtm, Cst,
Zrn

in bold – examined in detail; + rare, ++ common, +++ abundant
AGM – aeschynite-group minerals, EGM – euxenite-group minerals, CGM – columbite-group minerals, FGM – fergusonite-group minerals, SGM– samarskite-group minerals, PGM – pyrochlore-group minerals
1 – Škoda and Novák (2007), 2 – Škoda et al. (2006), 3 – Novák et al. (2011), 4 – Čopjaková et al. (2013), 5 – Novák and Filip (2010), 6 – Staněk
(1973), 7 – Čopjaková et al. (2015), 8 – Němec (1990), 9 – Novák et al. (2012), 10 – Novák et al. (1999), 11 – Novák (2005)

156

Beryllium minerals from NYF pegmatites of the Třebíč Pluton

tourmaline occur in the aplite, coarse-grained, and blocky
pegmatite units: rare prismatic crystals to anhedral grains
and their aggregates, graphic intergrowths with quartz
and common, interstitial fillings (for more details see
Novák et al. 2011; Čopjaková et al. 2013). Also, REE,
Nb, Ta, Ti-oxide minerals, and allanite-(Ce) were foundat most localities, whereas titanite and ilmenite occur
mainly in pegmatites where tourmaline is rare. Less common Sn-minerals (cassiterite, herzenbergite, stokesite),columbite group minerals and Nb-rutile are typical forthe most evolved pegmatites (e.g., Číměř I, Kožichovice
II). Apatite and REE-phosphates, monazite-(Ce) andxenotime-(Y), are very rare (Tab. 1).

4.2. Mineral assemblages and textural
relations of primary and secondary
Be-minerals
The detailed study revealed new mineral assemblages ofprimary and secondary Be-minerals different from thosedescribed to date by Staněk (1973), Škoda et al. (2006),
and Novák and Filip (2010). Three distinct paragenetic
types of Be-minerals were defined: type I – primarymagmatic Be minerals in massive pegmatite: beryl I,
phenakite I, and helvite-danalite I; type II – rare primaryhydrothermal minerals from miarolitic pockets: beryl II,
phenakite II; type III – proximal secondary hydrothermal minerals directly replacing primary Be-minerals
and distal ones filling fractures or small secondary vugs
near primary Be-minerals: beryl III, phenakite III, milarite–agakhanovite III, bohseite–bavenite series III, andbazzite III. Rare quartz + adularia veinlets/masses withmilarite–agakhanovite III and gadolinite-group mineral
III belong to the type III. However, their paragenetic
position and origin are worth for more detailed study.
Note, the suffix (I, II, III) indicates the paragenetic typeand not the generation of the mineral.

4.2.1. Primary minerals
We used the designation “a primary Be-mineral” for all
Be-minerals, which crystallized ambiguously during the
primary (magmatic) stage. They appear in the euhedral
to subhedral crystals, and their aggregates are embedded
in a massive pegmatite. They include beryl I, phenakite I,
helvite-danalite I (Tab. 1). Furthermore, very rare euhedral beryl II and phenakite II that crystallized into opened
miarolitic cavities (Tab. 2) are considered as minerals of
primary origin as well.
Primary minerals in the euxenite-type pegmatites(beryl I ~ helvite-danalite I > phenakite I) are commonly
enclosed in central parts of the dikes in a coarse-grained
pegmatite (blocky Kfs+Qz+Ab; beryl, helvite-danalite,
phenakite), in massive quartz (phenakite), in masses ofalbite (beryl), scarcely in the graphic unit (helvite-danalite) and in rare primary pockets (beryl II, phenakite II;
Tab. 2). In beryl pegmatites, beryl I forms pale green toyellowish prismatic crystals, up to 8 cm long and 5 mm
thick, and their radial aggregates. Chloritized phlogopite,aeschynite-group minerals, and pyrite were found closely
associated with or enclosed in some beryl crystals. In
the BSE images and thin sections, primary beryl I forms
elongated prismatic crystals with well-developed zoning (Fig. 3a). Microscopic inclusions of clay minerals
and secondary Be-minerals (beryl III, bohseite-bavenite
series III, milarite III, bazzite III) in veinlets and nest
aggregates are common (Fig. 3b). Less abundant longprismatic crystals of colorless phenakite I, up to 3 cmlong and 0.5 cm thick (Tab. 1), are typically fresh comparing beryl I; however, due to their quartz-like appearance and mostly lack of alteration phenakite may beeasily overlooked.
Primary brown to red Fe-rich helvite I to Mn-richdanalite I was found in coarse-grained pegmatite (blocky
K-feldspar + Qz > Ab) and graphic unit (Kfs + Qz) as
subhedral grains up to 5 cm in size in helvite-danalite

Tab. 2 Paragenetic types of primary and secondary Be-minerals
Be-minerals         Primary    Massive pegmatite
MiarolesQz, KfsAb
I
I
II
Koz II, Okr, Poz I, Cim I
Koz II
Poz
Koz II, Cim I, Klu III
Cim I
Ter
Cim I, Cim II, Klu III
Cim I
Cim I
Cim I
Cim I
Krc
Krc

Paragenetic type
Beryl/beryl*
Phenakite/phenakite
Helvite-danalite/danalite
Milarite/milarite
Hingganite-(Y)Hambergite
BazziteBavenite-bohseite
Bertrandite* Secondary minerals in italics
data from Kracovice in Němec (1990)

Secondary
Proximal/distal
III
Koz I, Koz II, Cim I, Krc
Okr, Koz II
Cim I
Koz I, Koz II, Cim I, Klu III

Koz I, Koz II
Koz I, Koz II, Cim I, Klu III, Krc
Krc

157

Adam Zachař, Milan Novák, Radek Škoda

Boh III

Brl I
Brl I

Bvn III
Brl I

Brl I
Ab

A

Brl I

500 µmBvn IIIB

Mil III

200 µmHlv I

Boh III

Ph I

Hlv I
Apy

C

D

200 µmQz

Boh III
Ph I
500 µm
1000
µm

Tur
Brl I

Boh IIIMil III

Ttn
Ph I

E

500 µm

F

100 µmFig. 3 BSE images of primary Be-minerals from beryl pegmatites (A, B) and helvite-danalite pegmatites (C–F). A – zoned beryl I partly replacedby bavenite-bohseite, Kožichovice II. B – fans of bavenite-bohseite III and milarite III veinlets in beryl I, Kožichovice II. C – helvite-danalite I
rimmed by bohseite associating with arsenopyrite replaced by pharmacosiderite, Číměř I. D – euhedral phenakite I and helvite I altered to bohseite
III, Číměř I. E – phenakite I embedded in tourmaline and crosscut by Ta-titanite, Číměř I. F – milarite III replacing beryl I, in association withbohseite III, Číměř I.

158

Beryllium minerals from NYF pegmatites of the Třebíč Pluton

Kfs
Brl I
Bvn III

Bvn III

Brl I
A

Brl I

200 µmBrl III
B

200 µmPh III

Kfs

Brl I
Brl I

Brl I

Bz III
Bvn III

Brl I
C

100 µmD

1000 µm

Jrs
Qz

Fig. 4 BSE images of secondary Be-minerals from beryl pegmatites. A – beryl I replaced by bavenite-bohseite III along with termination of crystal,Kožichovice II. B – zoned beryl I crosscut by veinlets of beryl III, Kožichovice II. C – bazzite III laths enclosed in bavenite III veinlet, crosscutting
beryl I, Kožichovice II. D – euhedral beryl I in quartz replaced by K-feldspar, phenakite III and jarosite, Okrašovice.

pegmatites (Tab. 2). They are locally associated witharsenopyrite (Fig. 3c) and typically covered by black
Mn-oxides. Phenakite I can be present in association
with helvite-danalite (Fig. 3d), and tourmaline (Fig. 3e)or occurs solely in quartz from central parts of pegmatite
body as prismatic crystals, up to 15 mm long. Scarcely,
small relics (< 100 µm) of intensively corroded beryl I(Fig. 3f), which is replaced by milarite, were observed in
the association with phenakite I, adularia and bohseite–
bavenite III.
Both very rare yellowish beryl II and a colorless phenakite II occur in scarce primary miarolitic pockets. They
are lined with crystals of K-feldspar (locally amazonite),quartz and albite. The former as short prismatic crystals,
up to 5 mm long, and the latter as tabular crystals, up to 5
mm in size, respectively (Tab. 2; Staněk 1973).
Two principal mineral assemblages can be distinguished on the base of a dominant primary Be-mineralin euxenite-type pegmatites (disregarding scarce minerals
from pockets as beryl II, phenakite II). It is the BP assemblage (beryl I ± phenakite I) that occurs exclusively
in beryl pegmatites. On the other hand, the HDP assemblage (helvite-danalite I > phenakite I >>> ± berylI) is restricted to helvite-danalite pegmatites (Tab. 1).
Apart from different Be-minerals assemblage, a further
distinctive feature is a scarcity and abundance of magmatic tourmaline in beryl and helvite-danalite pegmatites,
respectively.

4.2.2. Secondary minerals
Beryl I from the BP assemblage is commonly replaced bybohseite III to rare bavenite III (bohseite-bavenite series)
as platy crystals or fine-grained filling of thin veinlets andsmall nests within beryl I grains or along their boundaries(Fig. 4a). Rare beryl III is known as veinlets in grains of159

Adam Zachař, Milan Novák, Radek Škoda

Tab. 3 Representative analyses of the beryl-group minerals
Assemblage
Locality

KOZ I
Brl I
2
63.62
0.00
12.96
0.31
0.10
2.61
0.06
0.03
1.11
1.57
0.44
0.14
1.35
13.12
2.17

KOZ II
Brl I
3
63.69
0.00
14.29
0.13
0.00
2.34
0.00
0.00
0.81
1.60
0.32
0.17
0.51
13.19
2.20

BP
POZ
Brl II
4
65.92
0.00
14.48
0.09
0.00
2.29
0.03
0.02
1.02
1.49
0.39
0.00
0.59
13.46
2.10

HDP
KOZ IIBrl III
5
65.95
0.00
15.64
0.22
0.00
1.54
0.09
0.06
0.37
1.33
0.04
0.08
0.09
13.62
1.97

KOZ IIBz III
6
58.37
0.10
2.15
13.17
0.05
3.04
2.50
0.26
1.45
2.36
0.01
0.00
0.38
12.41
2.84

KOZ IIBz III
7
58.82
0.00
0.17
15.81
0.10
2.56
0.36
0.26
1.93
2.24
0.00
0.12
0.81
12.29
2.74

ČIM I
Brl I
8
65.34
0.00
15.97
0.00
0.00
0.70
0.05
0.00
1.41
0.89
0.00
0.09
0.22
13.25
1.59

ČIM I
Brl I
9
63.72
0.00
12.86
0.00
0.00
2.03
0.32
0.00
3.55
1.74
0.13
n.d.
n.d.
13.26
2.32

Total
101.2099.60
99.29
102.06100.99
apfu
Si4+
6.000
6.000
6.000
6.000
6.000
Ti4+
0.000
0.000
0.000
0.000
0.000
Al3+
1.593
1.441
1.587
1.553
1.677
Sc3+
0.018
0.025
0.010
0.007
0.017
V3+
0.001
0.007
0.000
0.000
0.000
Mg2+
0.302
0.367
0.329
0.311
0.209
Ca2+
0.000
0.006
0.000
0.003
0.009
Mn2+
0.004
0.002
0.000
0.002
0.005
Fe2+
0.087
0.088
0.064
0.078
0.028
Na+
0.222
0.287
0.292
0.263
0.235
K+
0.042
0.053
0.038
0.045
0.005
Rb+
0.008
0.008
0.010
0.000
0.005
Cs+
0.044
0.054
0.020
0.023
0.003
Be2+
3
3
3
3
3
H+
1.166
1.379
1.383
1.286
1.205
O2–
17.96417.94417.97917.94917.916
n.d. – non determined* calculated from ideal stoichiometry** based on the premise of H2O = 0.84958 × Na2O + 0.8373 (Giuliani et al. 1997)

99.04

98.19

99.75

99.93

6.000
0.008
0.260
1.180
0.004
0.466
0.275
0.023
0.125
0.470
0.001
0.007
0.017
3
1.935
18.253

6.000
0.000
0.021
1.405
0.007
0.390
0.040
0.022
0.165
0.443
0.000
0.008
0.035
3
1.864
17.999

6.000
0.000
1.729
0.000
0.000
0.096
0.005
0.000
0.108
0.158
0.000
0.005
0.009
3
0.985
17.955

6.000
0.000
1.427
0.002
0.000
0.284
0.032
0.009
0.280
0.318
0.016
n.d.
n.d.
3
1.458
17.921

SiO2
TiO2
Al2O3
Sc2O3
V 2O 3MgO
CaO
MnO
FeOtot
Na2O
K 2O
Rb2O
Cs2O
*BeO
**H2O

OKR
Brl I
1
64.80
0.00
14.59
0.23
0.01
2.19
0.00
0.05
1.13
1.24
0.36
0.14
1.12
13.51
1.89

beryl I (Fig. 4b), prismatic crystals, up to 100 µm long, inbohseite-bavenite aggregates and as thin alteration zones
between beryl I and secondary bohseite–bavenite masses.
Rare prismatic crystals of bazzite III, up to 50 µm long
(Fig. 4c), are typically embedded in some bohseite–
bavenite aggregates in beryl I (see also Novák and Filip
2010). Chlorites, epidote-clinozoisite, albite, and quartz
are locally associated mainly with minerals of bohseitebavenite series. Milarite III is typically located in quartzand phenakite-hosted cavities and locally is crosscut bybohseite III veinlets. Rare phenakite III forms veinlets inberyl I locally associated with late K-feldspar (Fig. 4d).
In the HDP assemblage, helvite-danalite I is altered toabundant bohseite III to rare Al-poor bavenite III (Figs
160

5a, b). They associate with axinite, which fills fissuresand voids distally from the altered helvite-danalite. Scarcedanalite III partially replaces and fills secondary vugs inprimary helvite I, and no other associated secondary Beminerals have been observed (Fig. 5c). Phenakite I and
Fig. 5 BSE images of secondary Be-minerals helvite-danalite pegmatites. A – helvite-danalite I replaced by bohseite III, Číměř I.
B – bohseite III fills the euhedral cavity in helvite-danalite I, Číměř I.
C – helvite-danalite I replaced by Zn-rich danalite III, Číměř I. D – zoned (REE-) milarite III in porous quartz veinlet, Číměř I. E – bohseite
III aggregate in the cavity, Číměř I. F – bohseite III penetrating phenakite I, Klučov III. G – milarite-agakhanovite (Mil III) overgrowths
on pyrochlore (Pcl), Číměř I. H – sector-zoning of gadolinite-groupmineral, Číměř I.

Beryllium minerals from NYF pegmatites of the Třebíč Pluton

Hlv I

Boh III

Boh III
Hlv I
AB

200 µm200 µmQz

Hlv III

Hlv I

C

Mil IIIQz

D

500 µm200 µmPh I

Boh IIIE

Boh IIIQz

Kfs F

500 µm200 µmQz

Kfs
Mil III

Qz
Qz

Pcl

Pcl

G

200 µm

H
B

100
100µm
µm
161

Adam Zachař, Milan Novák, Radek Škoda

Ca

0.1
0.2
0.3
0.4
0.5
0.6
0.7

0.9
0.8
0.7
0.6
0.5
0.4

0.9

0.2

0.0 1.0
0.1
0.9

0.2

0.8

0.3

0.7

0.4

0.6

0.5

0.5

0.6

0.4

0.7

0.3

0.8

Al

BP assemblage
KOZ-I Brl I
KOZ-II Brl I
OKR Brl I
POZ Brl II
KOZ-II Brl III
KOZ-I Bz III
KOZ-II Bz III
HDP assemblage
CIM-I Brl I

0.0 1.0

0.3

0.8

0.2

0.9

0.1
1.0
0.0
vac.0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 R+

0.1
1.0
0.0
M2+ 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Sc

very rare beryl I is typically altered to milarite III to rareagakhanovite-(Y) III (Fig. 5d) and bohseite-bavenite III(Fig. 5e). They replace, partially to almost wholly phenakite crystals. Also, they fill thin cracks in phenakite I or fillveinlets and small voids distal from phenakite. Commonly,
they are associated with late-stage quartz, adularia, andlocally also with axinite and rare REE-rich epidote (Fig.
5f). REE-rich milarite III to agakhanovite-(Y) III, which
overgrows anhedral cubic crystals of REE-rich pyrochlores.l. (Fig. 5g), is a further paragenetic type related to thequartz + adularia assemblage. Unfrequent euhedral crystalsof gadolinite-group minerals III, having less than 50 µm
across (Fig. 5h), are embedded in late quartz, adularia,
or milarite III, as well. Textural relations indicate thatformation of danalite III, milarite- and gadolinite-groupminerals, and adularia + quartz preceded the formation ofbohseite-bavenite series.

Rare beryl I from the HDP assemblage is also enriched in
Na (0.32–0.40 apfu), Fe and Mg (≤ 0.11–0.28, 0.21–0.28
apfu, respectively) but Sc-free. Bazzite III shows extreme
enrichment in Na (≤ 0.5 apfu) and Mg (≤ 0.6 apfu) andlocally also Ca (≤ 0.3 apfu) but is Al-poor (0.02–0.26
apfu). An average empirical formula could be expressed as(Na0.5Ca0.1Cs0.1□0.3)Σ1.0(Sc1.1Mg0.5Fe0.2Mn0.1Al0.1)Σ2.0Be3Si6O18.
Chemical composition of all types of phenakite I, II
and III is very close to the ideal formula (Tab. 3), only
traces of FeO (< 0.32 wt.%), MnO (< 0.13 wt.%) andNa2O (< 0.07 wt.%) were found.
Chemical analyses of primary helvite-danalite (Fig. 7,
Tab. 4) gave dominant Fe-rich helvite I to Mn-rich danalite I with 0.40–0.60 of Mn/(Mn + Fe), low concentrationsof Zn (0.07–0.11 apfu) and Mg (≤ 0.02 apfu). The minor
secondary Mn-rich danalite III with 0.38–0.40 of Mn/(Mn+Fe) has distinctively elevated Zn (0.33–0.51 apfu).
Secondary milarite III replacing phenakite, intergrowing with adularia, or penetrating helvite-danalite usually
has ~1 apfu Al, low Fe, Mn, and Sc typically ≤ 0.1 apfu
and REE below the detection limit of EPMA; it is close
to milarite s.s. On the other hand, the milarite-group min-Fig. 6 Chemical variation of beryl (Brl) and bazzite (Bz).

4.3. Chemical composition of Be-minerals
and associated tourmaline
Beryl I and II from all studied pegmatites are chemically heterogeneous but very similar (Figs 3a,b, 6, Tab. 3),
showing Al (1.45–1.74 apfu), Sc (≤ 0.06 apfu), Mg(0.21–0.39 apfu), Fetot (0.03–0.14 apfu), Na (0.17–0.34
apfu), and low concentrations of K (≤ 0.07 apfu) and Rb(≤ 0.01 apfu). Elevated Cs (≤ 0.15 apfu) caused the zoningof primary beryl I in the BSE images (Figs. 3a,b). The
concentrations of Sc increase gradually from the center
to the rim, whereas Fe exhibits an opposite trend. Cesium
is concentrated along with the prismatic faces, whereas
the outermost terminal parts of crystals are inferior inCs (see Fig. 3a). LA-ICP-MS data in beryl I from theKožichovice II pegmatite yielded Li ≤ 80, Sc 477–2446,
Ti ≤ 89, V 20–112, Ni ≤ 38, Zn ≤ 48, Ga ≤ 40, Rb 257–604,
Sn ≤ 18, Cs 2741–26973 ppm (Novák and Filip 2010).
162

CIM-I Hlv I
CIM-I Hlv III
CIM-II Hlv I
KLU-III Hlv I
0.5

Zn

0.6
0.7
0.8
0.9

0.5
0.4
0.3
0.2

0.1
1.0
0.0
Mn 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Fe
Fig. 7 Chemical composition of helvite–danalite.

Beryllium minerals from NYF pegmatites of the Třebíč Pluton

Tab. 4 Representative analyses of helvite–danalite
CIM-I
Hlv I
1
32.78
0.00
0.00
27.77
21.54
1.76
13.64
5.19
–2.59
100.08

CIM-I
Hlv I
2
33.66
0.05
0.00
22.75
26.84
1.31
14.01
5.14
–2.56
101.19

SiO2
MgO
CaO
MnO
FeO
ZnO
BeO
S
O=S
Total
apfu
Si4+
3.000
3.000
Mg2+
0.000
0.007
Ca2+
0.000
0.000
Mn2+
2.152
1.717
Fe2+
1.649
2.001
Zn2+
0.119
0.086
Be2+
3.000
3.000
S2–
0.889
0.858
O2–
12.03111.953mol. %
dan
42.06
52.69
hlv
54.90
45.05
gth
3.04
2.26
dan – danalite; hlv – helvite; gth – genthelvite

CIM-I
Hlv III
3
32.66
0.09
0.00
16.92
27.95
7.35
13.59
5.10
–2.54
101.12

CIM-II
Hlv I
4
32.13
0.00
0.00
21.33
30.45
0.63
13.37
5.59
–2.79
100.72

CIM-II
Hlv I
5
31.94
0.00
0.00
27.86
22.52
1.11
13.29
5.89
–2.94
99.67

KLU-III
Hlv I
6
32.07
0.00
0.00
26.20
24.63
1.48
13.35
5.61
–2.80
100.54KLU-III
Hlv I
7
32.67
0.00
0.00
23.40
26.63
1.61
13.60
4.92
–2.46
100.37

3.000
0.012
0.000
1.317
2.142
0.499
3.000
0.877
12.093

3.000
0.000
0.000
1.687
2.378
0.043
3.000
0.979
12.129

3.000
0.000
0.000
2.216
1.769
0.077
3.000
1.038
12.024

3.000
0.000
0.000
2.076
1.927
0.102
3.000
0.984
12.121

3.000
0.000
0.000
1.821
2.045
0.109
3.000
0.847
12.128

54.32
33.13
12.55

57.88
41.07
1.05

43.54
54.57
1.89

46.94
50.57
2.49

51.45
45.80
2.75

eral III, closely associated with REE-rich pyrochlore s.l.,contains a low amount of Al (0.36–0.44 apfu) and moderate content of Y (0.39–0.47 apfu), along with minor
Ln (≤ 0.1 apfu Ln) (Electronic supplementary material,
ESM 1). It suggests a transitional composition between
milarite s.s., and agakhanovite-(Y) with 22–55 mol. %of agakhanovite-(Y) component, and thus corresponds
to REE-rich milarite to agakhanovite-(Y).
Composition of the gadolinite-group mineral (Fig. 3f,
ESM 1) is variable; the analyses yielded 0.79–1.05 apfu
Ca, 0.62–0.85 apfu Y, 0.20–0.40 apfu Ln (Nd > Gd > Sm),
0.46–0.48 apfu of Fe and traces of Mg and Mn (≤ 0.02
apfu), see Fig. 8. Such composition is challenging to beclassified without direct determination of Be and B content. Common primary tourmaline, secondary tourmaline
after helvite-danalite I, and hydrothermal axinite suggest
high activity of B in the system, including pegmatite melt
and residual fluids. Hence, we can expect the availabilityof B during crystallization of gadolinite-group mineral andthus, its possible entrance along with Be into the structure(Cámara et al. 2008; Bačík et al. 2017). Using the general formula of gadolinite group A2MQ2(SiO4)2(O,OH)2,
where A = Ca, REE; M = Fe, Mn, Mg, □ and Q = B, Be(Bačík et al. 2017). Its chemical composition falls in thecenter of quadrilateral diagram REE/(Ca+REE) vs. R2+/
(R2+ + vacancy) and thus corresponds to an intermedi-

ate composition of either hingganite-(Y)–homilite orgadolinite-(Y)–datolite solid solutions. Keeping the nomenclature formalism for the gadolinite-group minerals(Bačík et al. 2017), domains brighter in BSE fall to theCa-, and Fe-rich hingganite-(Y) compositional field andthe darker domains correspond to □-, and REE-rich homilite. The calculated content of Be and B are 0.95–1.21 and
0.79–1.05 apfu, respectively (ESM 1).
1.0
0.8
R2+/(vac.+R2+)

Samplegadolinite

homilitehingganite

datolite

0.6
0.4
0.2
0.0
0.0

Číměř
Heftetjern
0.2
0.4
0.6
Ca/(Ca+REE)

0.8

1.0

Fig. 8 Chemical composition of gadolinite-group mineral from Číměř I(this study) and Heftetjern pegmatites (Cooper et al. 2019).

163

Adam Zachař, Milan Novák, Radek Škoda

Tab. 5 Representative analyses of minerals of bavenite–bohseite series
Precursor
Locality

Brl I
KOZ-II
1
58.60
4.80
23.81
0.06
0.00
0.28
0.22
8.48
3.01
–0.09
99.18

Brl I
KOZ II
2
57.78
4.09
23.68
0.04
0.03
0.26
0.25
8.68
3.01
–0.11
97.71

SiO2
Al2O3
CaO
MnO
FeO
Na2O
F
*BeO
**H2O
O=F
Total
apfu
Si4+
9.000
9.000
Al3+
0.869
0.751
Ca2+
3.919
3.952
Mn2+
0.008
0.005
Fe2+
0.000
0.004
Na+
0.085
0.079
F0.109
0.123
Be2+
3.131
3.249
OH–
3.084
3.125
O2–
24.80726.376* calculated from stoichiometry** calculated from charge balance

Hlv I
CIM-I
3
58.82
1.93
24.07
0.35
0.26
0.16
0.20
9.93
3.38
–0.08
99.02

Hlv I
CIM-I
4
59.35
5.48
24.17
0.00
0.00
0.11
0.20
8.29
3.00
–0.09
100.52

9.000
0.349
3.946
0.045
0.033
0.049
0.097
3.651
3.457
24.446

9.000
0.979
3.928
0.000
0.000
0.033
0.097
3.021
3.035
24.868Minerals of bavenite-bohseite series have the general formula Ca 4Be 2+xAl 2–xSi 9O 28–x(OH) 2+x, where x < 1
for bavenite and x > 1 for bohseite (Friis et al. 2010).
Their chemical composition from the studied pegmatites is highly variable (Tab. 5). Bavenite to Al-richbohseite is related to replacement of beryl I (BP assemblage) and contain 0.75–1.13 apfu Al (4.09–5.85 wt. %Al2O3) (Fig. 9). In the HDP assemblage, the minerals ofbohseite-bavenite series after helvite-danalite I shows
0.36–1.05 apfu Al (1.93–5.48 wt. % Al 2O 3) and en4.0

Locality:
CIM II
KOZ IIKLU III

3.8

Be (apfu)

3.6
3.4
3.2

Precursor:
phenakite
3.0
helvite-danalite
beryl
2.8
0.0

0.2

0.4

0.6

Al (apfu)

0.8

1.0

1.2

Fig. 9 Variation of Al-content in bavenite–bohseite series reflecting thevariable amount of Al in their precursor.

164

richment in Fe and Mn (≤ 0.1
apfu). Fissures-filling bohseite
Phk I
Phk I
III related to phenakite I alteraCIM-I
KLU-IIItion has very low Al (0.16–0.77
56
apfu; 0.85–4.34 wt. % Al2O3),
59.48
58.88
2.50
0.85
and elevated F (≤ 0.3 apfu). Rare
24.58
25.16
bohseite-bavenite after milarite
0.00
0.11
I provided 0.82–1.02 apfu Al
0.00
0.00
(4.14–5.67 wt. % Al2O3).
0.11
0.12
Typical features of tour0.22
0.54
maline from the Třebíč Plu9.77
10.48
ton euxenite-type pegmatites
3.41
3.22
is their low Al content (~5–6.4
–0.09
–0.23
apfu) and mostly low vacancy in
99.98
99.13
the X-site (Novák et al. 2011).
Tourmalines (schorl-dravite)
9.000
9.000
from beryl and helvite-danalite
0.446
0.153
3.985
4.121
pegmatites show low Al ~5–6
0.000
0.015
apfu and variable Fe/(Fe + Mg)
0.000
0.000
= 0.28–0.96 higher in the latter
0.033
0.035
(Fig. 10, Tab. 6). In beryl peg0.104
0.260
matites, scarce tourmaline oc3.554
3.847
curs in the outer pegmatite unit,
3.447
3.281
or it is a late fracture-filling type24.44924.459(see Novák et al. 2011) whereas
in helvite-danalite pegmatites
abundant tourmaline crystallized
from outer to central pegmatite units.

5. Discussion

5.1. Chemical composition of Be-minerals
Data on chemical composition of beryl from NYF pegmatites are rather scarce (e.g., Aurisicchio et al. 1988;
Novák and Filip 2010; Přikryl et al. 2014), compared
to e.g., LCT pegmatites (Černý et al. 2003; Wang et al.
2009; Uher et al. 2010, 2017; Aurisicchio et al. 2012).
Chemical composition of primary beryl I and II from all
examined localities of euxenite-type pegmatites in theTřebíč Pluton (Tab. 3, Fig. 6) are very similar. It is also inline with the composition of beryl from the Kožichovice
II pegmatite (Tab. 1) studied in detail by Novák and Filip(2010). Beryl from the Třebíč pegmatites is Mg-rich (Mg> Fe) and high contents of Mg, Sc and Cs reflect the highconcentrations of these elements in parental durbachite of
the Třebíč Pluton (Novák et al. 2012). Moreover, it also
reflects their concentrations in the residual melt fromwhich the pegmatites formed. Substantial octahedral substitution is indicated by rather low Al and elevated R2+,
and the charge is balanced by entering of R+ into channels(Fig. 6). Not only the high contents of Mg in beryl, butalso in other minerals (tourmaline, biotite) from Třebíč

Beryllium minerals from NYF pegmatites of the Třebíč Pluton

Al

vac.

0.0 1.0

0.1
0.2
0.3
0.4
0.5

Beryl pegmatites
KOZ-II
OKR
POZ
Hlv-dan pegmatites
CIM-I
CIM-IIKLU-III

0.9
0.8
0.7
0.6
0.5

0.6

0.3

0.8

0.9

0.2

0.8
0.7

0.4

0.2

0.9

0.1

0.3

0.4

0.7

0.0 1.0

0.1
0.5
1.0
0.0
Na+K 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Ca Fetot 0.0

0.6

0.1

0.2

0.3

0.4

0.5
0.5 MgFig. 10 Chemical composition of tourmaline from TP euxenite-subtype pegmatites.

Tab. 6 Chemical composition of tourmaline from euxenite-subtype pegmatites of the Třebíč Pluton
KOZ-II
1
35.48
3.01
26.31
2.94
6.35
1.80
0.34
7.63
2.01
0.08
10.28
3.20
0.22
–0.11
99.54

Beryl-bearing pegmatites
POZ
2
36.51
0.33
30.66
2.64
5.65
0.74
0.13
6.87
2.24
0.05
10.58
3.83
0.17
–0.09
100.31

OKR
3#
35.69
2.71
26.24
1.95
7.81
1.97
0.15
7.03
1.94
0.05
10.34
3.42
0.25
–0.11
99.44

CIM-I
4
34.14
4.06
25.49
4.41
3.50
0.88
0.32
11.45
2.40
0.08
9.89
2.13
0.31
–0.16
98.90

Helvite-bearing pegmatites
CIM-I
CIM-II
5
6
34.58
34.50
1.16
2.74
28.25
25.68
3.40
4.68
4.68
3.06
0.66
0.33
0.21
0.51
8.84
12.16
2.32
2.13
0.04
0.03
10.01
9.99
2.92
2.97
0.29
0.42
–0.15
–0.22
97.21
98.97

SiO2
TiO2
Al2O3
†
Fe2O3
MgO
CaO
MnO
FeOtot
Na2O
K 2O
*B2O3
*H2O
F
–O = F
Total
apfu
Si4+
6.000
6.000
6.000
6.000
6.000
6.000
Ti4+
0.383
0.041
0.342
0.537
0.152
0.358
Al3+
5.247
5.939
5.200
5.281
5.779
5.264
Fe3+
0.374
0.327
0.247
0.583
0.444
0.612
Mg2+
1.602
1.384
1.957
0.918
1.209
0.792
Ca2+
0.326
0.131
0.356
0.166
0.123
0.062
Mn2+
0.049
0.018
0.021
0.047
0.031
0.075
Fe2+
1.121
0.981
0.988
1.749
1.332
1.836
Na+
0.659
0.713
0.632
0.818
0.782
0.718
K+
0.017
0.010
0.012
0.017
0.009
0.006
B3+
3.000
3.000
3.000
3.000
3.000
3.000
OH–
3.611
3.912
3.830
2.498
3.381
3.449
F–
0.117
0.088
0.135
0.172
0.161
0.232
O2–
27.27227.00027.03528.33027.45827.319† calculated as 25% from Fetot, estimated by Mössbauer spectroscopy in similar pegmatites of TP (see Novák et al. 2011)* calculation based on ideal stoichiometry#
from Novák et al. (2011)

KLU-III
7
35.47
3.65
26.64
3.88
4.17
1.01
0.37
10.09
2.46
0.10
10.27
2.87
0.21
–0.10
101.09
6.000
0.464
5.312
0.494
1.051
0.183
0.053
1.482
0.807
0.022
3.000
3.243
0.110
27.647165

Adam Zachař, Milan Novák, Radek Škoda

pegmatites, make them distinct from typical NYF pegmatites. Therefore those, where beryl is rich in Fe (Fe >Mg) (Aurisicchio et al. 1988; Přikryl et al. 2014) as other
Fe,Mn,Mg-minerals (Falster et al. 2012, 2018). Bazzite
III shows extreme enrichment in Na (≤ 0.5 apfu), Mg(≤ 0.6 apfu) and Fe (≤ 0.2 apfu) and locally also Ca (≤ 0.3
apfu). Part of the most Na-, Mg-, and Fe-rich analyses
reaches the compositional field of a possible new mineral
species of the beryl group (Fig. 6) with a general formula
A+1Sc1M2+1Be3Si6O18.
Helvite-group minerals from NYF pegmatites ofTřebíč Pluton include Fe-rich helvite I to Mn-rich danalite I, Mn/(Mn+Fe) = 0.4–0.6, and locally, secondary
Mn-rich danalite III enriched in Zn (≤ 0.51 apfu) with
Mn/(Mn+Fe) ~ 0.4. Despite an abundance of Mg in thepegmatite melt, its concentration in helvite is very low(Tab. 4). Such low Mg content is typical for all helvitegroup minerals reported in the literature (e.g., Dunn 1976;
Barton and Young 2002) and thus an entrance of Mg to
the helvite-danalite structure is controlled by crystalstructural constrains. At the Třebíč pegmatites, elevatedMn and a very low Mg in magmatic helvite-group minerals are in contrast with the overall composition of mafic
minerals from the examined pegmatites. Tourmaline is adominant primary mafic mineral in helvite-danalite pegmatites, and its composition (Fig. 10, Tab. 6) reflects highcompatibility of Mg and incompatibility of Mn with thetourmaline structure (Henry et al. 2011). Crystallizationof large portions of tourmaline resulted in enrichment of
the ongoing melt in Mn, which facilitated the formationof helvite to Mn-rich danalite. Despite this, the chemicalcomposition of primary helvite-group minerals differsfrom most granitic pegmatites where Fe-poor helvite(e.g., Barton and Young 2002; Černý 2002) and locallyZn-rich to genthelvite (Glass and Adams 1953; Zito andHanson 2017; Larsen 1988) are typical.
The mineral of milarite group (Fig. 5g) with low Al(0.36–0.44 apfu) and moderate Y (0.39–0.47 apfu) alongwith minor amounts of Ln (≤ 0.1 apfu) (ESM 1) is transitional between agakhanovite-(Y) and milarite s.s. The
similar composition was found in late milarite from NYF
pegmatite Velká skála, Písek (see Novák et al. 2017 fordetails) where rather high Y and low Al are typical. Secondary milarite III after helvite-danalite or phenakite with
Al~1 apfu, low Fe, Mn and Sc ≤ 0.1 apfu and REE-free
is similar to secondary milarite from granitic pegmatites(Černý 2002) but also to primary milarite I from the
Velká skála pegmatite (Novák et al. 2017). Agakhanovite(Y) from the type locality Heftetjern, Norway, fills small
miarolitic cavities as a product of late hydrothermal solutions (Hawthorne et al. 2014). Hence, the chemical composition of milarite-group minerals, in particular, reflects
local enrichment of some elements than its paragenetic
position within certain granitic pegmatite.
166

Chemical composition of gadolinite-group minerals
falls to an intermediate composition among gadolinite(Y), hingganite-(Y), datolite, and homilite (see ESM 1)
showing roughly half occupancy of M-site and amountsof ~ 0.5 Ca/(Ca+REE). Calcium-rich hingganite-(Y) witha chemical composition close to those from Číměř I isreported by Cooper et al. (2019) from Heftetjern granitic
pegmatite, Norway, where it forms small crystals of hydrothermal origin the late-stage vugs. Such compositions
are far from typical, early magmatic gadolinite known
from granitic pegmatites Baveno, Italy (Pezzotta et al.
1999), Ytterby, Sweden (Smeds 1990), White Cloud,Colorado (Henry 2013) where A-site is predominantly
occupied by HREE, Fe is dominating over □ and Be >B. Consequently, an elevated M-site vacancy could beconsidered as an indicator of the hydrothermal originof gadolinite-group minerals in granitic systems andthe compositional shift towards datolite gives evidence
for elevated Ca and B activity. The chemistry roughly
corresponds to an insufficiently described mineral calcybeborsilite (see Rastsvetaeva et al. 1996) from the boronrich alkaline pegmatite Dara-i-Pioz, Tajikistan where it
seems to be of a magmatic origin (Pekov et al. 2000).
The chemical composition of bohseite-bavenite series ishighly variable with high Al (0.75–1.06 apfu) in replacement products of beryl I and milarite I and moderate to
low Al (0.16–1.05 apfu) in bohseite filling fractures inhelvite-danalite I and particularly after phenakite I. Sucha high variability and particularly dominance of bohseite
after bavenite is unusual (Szełęg et al. 2017). Regarding
Al-contents, they decrease from Al-rich, beryl-hosted
to Al-poor, phenakite-hosted environments (Zachař andŠkoda 2019).

5.2. Paragenetic position of primary
Be-minerals and mineral replacement
reactions
Beryllium-minerals as euhedral to subhedral crystals andtheir aggregates enclosed in a massive pegmatite (beryl I,
phenakite I, and helvite-danalite I) crystallized at the
primary (magmatic) stage. Similar morphologies andmineral assemblages are known from elsewhere (London
2008). High variability in primary Be-minerals, including
beryl, phenakite, and helvite-danalite is reflected in themineral assemblages of secondary Be-minerals and theirchemical composition. The following replacement paths
were observed:1) beryl I → bohseite-bavenite III + beryl III+ bazzite III + smectite (Novák and Filip 2010)2) beryl I → bohseite-bavenite III + clinozoisite
3) beryl I → phenakite III + K-feldspar + jarosite4) phenakite I → milarite III5) phenakite I → bohseite III

Beryllium minerals from NYF pegmatites of the Třebíč Pluton

6) helvite-danalite I → helvite-danalite III7) helvite-danalite I → bohseite III ± ferroor mangan-axinite
Alterations of beryl I (reactions 1–3) are limited to
the BP assemblage. Reaction 1) and 2) are typical for theKožichovice II pegmatite, whereas path 3) was observed
exclusively in the Okrašovice pegmatite. The sequence of
crystallization of secondary Be-minerals is not easy to define in most examined samples. Beryl III from late veinlets in beryl I (Fig. 4b) is likely the earliest among thesecondary minerals, whereas bohseite-bavenite is mostly
the latest mineral. Phenakite I is resistant to any alterationin the BP assemblage. Reactions 4–7) are restricted to
the HDP assemblage. Phenakite replacements reactions
4) and 5) could take place at the same hand samples andreaction 4) preceded reaction 5). Helvite-danalite I iscommonly altered to bohseite III (reaction 7) or rarely
to helvite-danalite III (reaction 6). These reactions were
spatially and genetically separated, and textural featuresindicate that the formation of danalite III was a highertemperature event compared to the formation of bohseite
III (Fig. 5a, b). No replacements of earlier secondary
Be-minerals by later ones were observed either in berylor helvite-danalite pegmatites.

5.3. Geochemical conditions during theorigin of primary and secondary
Be-minerals in granitic pegmatites
Activity and P–T diagrams published by Barton (1986),
Barton and Young (2002), Franz and Morteani (2002)
and Markl (2001) illustrate that activities of Si and Al
and alkalinity/acidity are crucial for the stability of Beminerals along with activities of Fe, Mg, Mn, REE, P, B,
S, and fO2; consequently, geochemical potentials govern
the stability of Be-minerals in particular along with PT
conditions.
Primary Be-minerals may be used for elucidation ofactivities of elements and fluids in single pegmatites orwithin the individual pegmatite units. The by far mostabundant pegmatites with beryl as a sole primary Bemineral reflect its large stability field (Barton 1986;
Franz and Morteani 2002) but also peraluminous natureof most granitic pegmatites of the rare-element class(e.g., London 2008; Černý et al. 2012). Strongly peraluminous pegmatites also contain sole chrysoberyl or
the assemblage beryl + chrysoberyl (London 2008). The
Třebíč Pluton pegmatites with beryl (± phenakite) as asole primary Be-mineral (Tab. 1) are only slightly peraluminous, where Al-rich minerals (e.g., muscovite, garnet,
cordierite, andalusite) are absent and rare tourmaline has
Altot < 6 apfu (Fig. 10; Novák et al. 2011; Čopjaková etal. 2013). Thus, it may represent an Al-poor variety of

aforementioned peraluminous pegmatites. Berylliumbearing granitic pegmatites depleted in Al (slightly
peraluminous or metaluminous in composition) are lesscommon worldwide and the assemblage phenakite + berylor dominant phenakite are typical (e.g., Falster et al.
2012, 2018). Only the pegmatite Kožichovice II (Novák
and Filip 2010) is close to this type (Tab. 1).
If activities of some other cations are sufficiently highand activity of Al appropriately low, we can find primary
helvite-group minerals (Mn, Fe, low fO2), milarite-groupminerals (Ca, K, REE) and/or gadolinite-group minerals(REE, Fe). The helvite-danalite pegmatites locally withrare primary phenakite, milarite- and gadolinite-groupmineral from Číměř I, II and Klučov III (Tab. 1) are
examples of these metaluminous pegmatites with common Al-poor tourmaline (Fig. 10), where also low fO2 isevident from the abundance of sulfides (Tab. 1).
High activity of P, typically found in strongly peraluminous pegmatites, with contemporary elevated Be
is indicated by the presence of primary hurlbutite alongwith common apatite (Černý 2002); however, very low
contents of P in the Třebíč pegmatites manifested also by
low P in feldspars, and almost total absence of phosphates(Škoda et al. 2006) follow their metaluminous character.
High B in pegmatites promoted the formation of hambergite and/or rhodizite-group minerals (London 2008)
along with abundant Al-rich tourmaline, all typicallyassociated with beryl (e.g., Novák et al. 2015). Such conditions were found in the Kracovice pegmatite. However,primary beryl has not been found at this pegmatite, andorigin of borates from melt requires elevated alkalinity(e.g., Novák and Povondra 1995; Novák et al. 1998;
London 2005, 2008).
Secondary Be-minerals show distinct mineral assemblages in beryl pegmatites (BP assemblage) andhelvite-danalite pegmatites (HDP assemblage). Variable contents of Al in primary Be-minerals are manifested very well in the secondary mineral assemblages.
Chemical composition of bohseite-bavenite III reflects
Al-contents of its precursor: after beryl I (0.75–1.06 Al
apfu), after helvite-danalite I (0.35–0.98 Al apfu) andafter phenakite I (0.16–0.75 Al apfu). The dominanceof minerals of bohseite-bavenite series over other secondary Be-minerals along with secondary milarite, also
shows high activity of Ca in hydrothermal fluids also
indicated by late axinite-(Fe,Mn), epidote-clinozoisite,
and titanite (Škoda et al. 2006; Novák and Filip 2010)
as well as neutral to alkaline conditions (Černý 2002).
These fluids were likely exsolved from pegmatite residual melt with the negligible role of external fluids
derived from host durbachite. It is manifested by theabsence or very low contents of Mg in most secondary
Be-minerals (see Novák et al. 2017) except for bazzite
III where Mg is likely sourced from altered primary167

Adam Zachař, Milan Novák, Radek Škoda

Mg-enriched beryl I (Tab. 3). Variations in the chemicalcomposition of bohseite-bavenite are controlled by thechemical composition of the precursor; Al-rich minerals
of bohseite-bavenite series formed after beryl whereas
Al-poor bohseite after phenakite. Aluminium content in
the fluids exsolved from melt, likely rather low (Buřival
and Novák 2018), was exhausted by formation Al-bearing
minerals (beryl III, adularia, axinite, epidote, clinozoisite,milarite) in early stages of hydrothermal replacements.
Its low mobility and negligible role during the bohseitebavenite formation is very likely. Hence, the chemicalcomposition of minerals of bohseite-bavenite series mirrors the chemical compositions of the replaced primaryphases in the local environment and shows low Al mobility at such conditions (Zachař and Škoda 2019).

5.4. Assemblages of primary
beryllium-minerals from NYF pegmatites
Beryllium-minerals are known from several NYF intragranitic pegmatites of durbachite plutons in the Moldanubian Zone: Třebíč Pluton, Western Moravia (Škoda
et al. 2006; Novák and Filip 2010), Mehelník Massif,
Central Bohemia (Novák et al. 2017) and Milevsko Pluton, Central Bohemia (Škoda et al. 2004; J. Cícha pers.
comm.) and display high variability. They show the evolution from relatively Al-rich assemblages in pegmatites
with common beryl and locally rare phenakite to Aldepleted assemblages in pegmatites with helvite-danalite,
phenakite, and very rare beryl. Two distinct trends in
Al-depleted assemblages are apparent. The assemblage
with dominant helvite-danalite ± minor phenakite is characterized by high activities of R2+ cations (Fe, Mn, Mg)
indicated along with common helvite-danalite by abundant tourmaline. In contrast, the Velká Skála pegmatitein the Mehelník Massif, with primary milarite is highly
leucocratic with rare biotite and tourmaline (Novák et al.
2017) which demonstrate low activities of Mg and Fe2+.
The assemblages of primary Be-minerals from thepegmatites of the Třebíč Pluton (Tabs 1, 2) show quite ahigh variability comparing other granitic pegmatites both
NYF and LCT affiliated. The most abundant primary Bemineral in NYF pegmatites is beryl (Černý 2002; Černý
and Ercit 2005). It is locally associated with phenakite(as e.g., in Erongo, Namibia; Falster et al. 2018), or ascarce phenakite is dominant primary Be-mineral alongwith very rare beryl (as in Nine Mile Pluton, Wausau,
Wisconsin; Falster et al. 2012), or it is a sole Be mineralat the locality (as in Tangen, Kragerø, Norway; Bjørlykke 1937). Helvite-group minerals scarcely occur in
LCT and NYF pegmatites, the most frequently as a latestage mineral in the vugs and less commonly as primarymagmatic or metasomatic phases. In general, helvite isprobably the most common, whereas genthelvite seems
168

to be less abundant. (Dunn 1976; Barton and Young
2002). Helvite-danalite from the Třebíč Pluton with Fe/
Mn close to 1 is rather unusual. Gadolinite-group minerals are further common primary Be-minerals in NYF
pegmatites occurring with beryl at some pegmatites (e.g.,
Baveno, Italy, Pezzotta et al. 1999; some pegmatites at
Evje-Iveland, Norway, Bjørlykke 1935; Müller et al.
2017; Høydalen, Norway, Chukanov et al. 2017; Ytterby,
Sweden, Simmons 2005) but it is often the only and arather common primary Be-mineral typically associatedwith some of following minerals: fluorite, magnetite,allanite, REE–Nb–Ta–Ti oxides, and vice-versa (e.g.,
White Cloud, Colorado, Simmons et al. 1987; Arvogno,
Alps, Guastoni et al. 2014, 2019; some pegmatites at
Evje-Iveland, Norway, Bjørlykke 1935; Åskagen, Sweden, Škoda et al. 2012; Reunavare, Sweden, Škoda et al.
2015). Primary milarite in granitic pegmatites is known
only from a single locality of the NYF pegmatite at Velká
Skála near Písek; however, due to the similar appearanceof milarite with beryl it may be easily overlooked (Novák
et al. 2017).
The mineral assemblages of primary Be-minerals(beryl, phenakite, helvite-danalite) plus secondary orhydrothermal phases (beryl, bazzite, phenakite, danalite,
milarite- and gadolinite-group minerals and bohseitebavenite) in a single pegmatite district (Třebíč Pluton)
are unusual. Hanson and Zito (2019) described similarassemblage (bazzite, helvite-group minerals, phenakite,bertrandite, and gadolinite-group minerals) from theMount Rosa Complex, Colorado Front Range, Colorado.
However, host rocks of Be-minerals include along withvariable miarolitic pegmatites, also quartz dikes, andalmost all Be-minerals occur in open vugs, and their primary origin is not documented sufficiently. The system
is also F-rich and differs significantly from F-poor euxenite-type pegmatites of the Třebíč Pluton. Disregarding
similar mineral assemblages of Be-minerals at the Mount
Rosa region (Hanson and Zito 2019), they are mostlyhydrothermal, whereas similar primary hydrothermal Beminerals from pockets in pegmatites of the Třebíč Pluton(beryl II, phenakite II, see Tab. 1) are very rare.

6. Conclusions
Beryl and helvite-danalite, major primary Be-minerals in
the euxenite-type pegmatites of Třebíč Pluton, were only
exceptionally found within a single pegmatite dike. It
suggests different activities of Al in the parental medium(beryl – high, helvite-danalite – low). Abundant tourmaline in pegmatites with helvite-danalite and its scarcity inberyl pegmatites indicate that tourmaline crystallization
may have controlled the formation of a primary Be-mineral. Such diverse assemblage of primary Be-minerals,Beryllium minerals from NYF pegmatites of the Třebíč Pluton

including beryl, helvite-danalite, and phenakite within asingle pegmatite district, is noteworthy.
Secondary Be-minerals with predominating bohseitebavenite series members and a minor secondary milariteand gadolinite group mineral indicate a high activity of
Ca in fluids. Variations in the chemical composition ofminerals of bohseite–bavenite series mirrors the chemical compositions of the replaced primary phases in thelocal environment and shows low Al mobility at suchconditions.
The assemblages of primary and secondary Be-minerals from pegmatites of the Třebíč Pluton manifest that theindividual assemblages are constrained by variable activities of Si and mainly Al, divalent cations – Ca, Mn, Fe,
Zn and Mg, and trivalent cations – REE, Sc; B, S and also
fO2 played a significant role in the formation of helvitegroup minerals (Barton and Young 2002; Franz and Morteani 2002). However, the individual primary Be-minerals
are not indicative of the explicit geochemical family of
granitic pegmatites except for gadolinite s.s. (NYF) andrhodizite, hurlbutite, and beryllonite (all LCT).
Acknowledgments The authors thank E. Szełęg and A. Guastoni for constructive criticism that significantly improved themanuscript and J. Plášil and J. Sejkora for excellent editorial
handling. The authors also thank and V. Hrazdil and S. Houzar from the Moravian Museum, Brno, for the samples ofberyl from Pozďátky II, phenakite from Terůvky and helpfulcomments. This work was supported by the research projectGAČR P210/19/05198S to MN and RŠ.
Electronic supplementary material. Supplementary tablecontaining analyses of milarite- and gadolinite-group minerals is available online at the Journal web site (http://dx.doi.org/10.3190/jgeosci.307).

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